1. Technical Field
The disclosure relates in general to a control system for a touch screen, and more particularly to a control system that, by utilizing a voltage-level shifter, converts a common voltage for driving a screen to a timing signal acceptable by a touch controller and accordingly controls a touch sensing timing.
2. Description of the Related Art
A touch screen combining touch sensing of a touch sensor and a display function of a screen provides a user-friendly and intuitive control interface, and is one of the most prevalent human-machine interfaces in the modern world.
FIG. 1 shows a sectional view of a conventional touch screen 10. The touch screen 10 engages a touch sensor 12 and a screen 14 via an adhesive layer ADVp. The touch sensor 12 includes a cover lens layer CLp, an adhesive layer OCAp, an electrode layer ITO_SRp, an isolating layer PET1p, an electrode layer ITO_SLD and an isolating layer PET2p. For example, the cover lens layer CLp is made of glass or acrylic, the adhesive layer OCAp is an optically clear adhesive layer, the electrode layers ITO_SRp and ITO_SLD are conductive layers formed from indium tin oxide (ITO), and the isolating layers PET1p and PET2p are non-conductive isolating layers formed by polyester films. The electrode layer ITO_SRp includes a plurality of sensing electrodes. When touch control occurs on the cover lens layer CLp, the sensing electrodes distributed at different positions are respectively coupled to capacitance changes in different values. Thus, a touch position can be determined according to the positions of the sensing electrodes and the capacitance changes coupled to the sensing electrodes.
For example, the screen 14 is a liquid crystal display (LCD) panel including an upper glass substrate TG, an electrode layer ITO_VCOMp and a liquid crystal structure LCSp. The electrode layer ITO_VCOMp is a conductive layer formed by ITO. The liquid crystal structure LCSp includes pixel electrodes in a matrix arrangement in another ITO electrode layer (not shown). Each of the pixel electrodes forms a pixel with a thin-film transistor (not shown), while liquid crystal is filled between the pixel electrodes and the electrode layer ITO_VCOMp. The electrode layer ITO_VCOMp extends along a planar direction of the screen 14 to cover the pixel electrodes of the screen to conduct a common voltage. Under the control of a gate voltage, the thin-film transistors conduct a source voltage to the corresponding pixel electrodes. Therefore, in the pixels, the source voltage conducted with the pixel electrodes drives the crystal liquid filled between the pixel electrodes and the electrode layer ITO_VCOMp together with the common voltage present on the electrode layer ITO_VCOMp to change a status of the liquid crystal. For example, an arrangement direction and thus a transparency of the liquid crystal is changed, allowing the pixels to present an image having different and distinct brightness and color.
As the liquid crystal is driven by a constant-polarity voltage in the long term, particle characteristics of the liquid crystals can be damaged to result in a residual image on the screen. To prevent the residual image, the common voltage transmitted on the electrode layer ITO_VCOMp periodically switches to different levels to perform polarity inversion. Since the touch sensor 12 is very much alike like the electrode layer ITO_VCOMp in the screen 14 and the electrode layer ITO_VCOMp has a substantial area, the conventional touch sensor 12 is required to be provided with a shielding electrode layer ITO_SLD, so as to prevent transition of the common voltage to be coupled to the sensing electrodes of the electrode layer ITO_SRp. In the absence of the electrode ITO_SLD, the transient state triggered by the transition of the common voltage shall be coupled to the sensing electrodes of the electrode layer ITO_SRp to undesirably affect touch sensing.